As is known, a propulsive assembly of an aircraft comprises an engine nacelle in which a motorization is arranged substantially concentrically. The engine nacelle comprises, at the front, an air inlet which is extended inside the engine nacelle by a duct for channeling the air towards the motorization.
In certain conditions, frost or ice can tend to form at the air inlet. This formation of frost or ice must be limited in order to avoid having blocks of ice ingested by the motorization and damaging it. To this end, the engine nacelle comprises a de-icing device. Hereinafter in the description, the term “de-icing” covers both treating frost and ice.
According to an embodiment known from the documents FR-2.813.581 and U.S. Pat. No. 6,443,395, illustrated in FIG. 1, an engine nacelle 10 comprises, inside, a partition called front frame 12 which delimits, with the air inlet 14, an annular duct 16 which is also called “D-duct” which extends over the entire circumference of the engine nacelle and which has an approximately D-shaped section.
This duct 16 comprises a hot air supply with at least one orifice 18 and one exhaust 20 for discharging the cooled air used for the de-icing.
The hot air is taken at an outlet 24 of a compressor stage of the motorization 22 and the hot air supply comprises a pipeline 26 for routing it to the orifice 18. This pipeline 26 comprises pressure measuring means 28 and means for regulating the pressure in order to deliver the requisite quantity of hot air at the orifice 18.
A motorization 22 comprises a plurality of outlets 24, 24′, 24″, each having a pressure/temperature pairing that is different from the others. The outlet 24 is chosen by establishing a trade-off between the hot air requirements for the de-icing and the structural and thermal capabilities of the air inlet 14. Thus, the air flow taken must have a high pressure and temperature to ensure effective de-icing. Conversely, an excessively high temperature and/or pressure can damage the air inlet which is generally produced from composite materials.
The means for regulating the pressure comprise a first pressure regulation valve 30 and a pressure regulation and stop valve 32.
The pressure regulation valve is controlled by a solenoid and can occupy two positions, a fully open position and a regulated position. This valve 30 is regulated pneumatically with a single pressure level.
The pressure regulation and stop valve 32 is controlled by two solenoids and can occupy three positions, a fully open position, a regulated position and a closed position. This valve 32 is regulated pneumatically with a single pressure level identical to that of the pressure regulation valve 30.
In the absence of any electrical signal, the pressure regulation and stop valve 32 occupies the fully open position whereas the regulation valve occupies the regulated position.
FIG. 2 schematically shows a pressure regulation and stop valve 32. The latter comprises a shutter 34 of butterfly type pivoting in the pipeline 26, which can, by pivoting about a rotation axis 36, occupy three positions, a fully open position (solid line), a regulated position and a closed position (broken lines).
The flow circulating in the pipeline 26 has a pressure Pam upstream of the shutter 34 and a pressure Pav downstream of the shutter 34.
The position of this shutter 34 is subjected to a rod of a piston 38 of an actuator 40 of pneumatic type which comprises two chambers separated by the piston, a control chamber 42 with a pressure Pc and a head chamber 44 with a pressure Pt. When the volume of the control chamber 42 increases, the rod of the piston provokes the rotation of the shutter 34 to the fully open position. When the volume of the control chamber 42 decreases, the rod of the piston provokes the rotation of the shutter 34 towards the closed position.
The control chamber 42 comprises a spring 45 which tends to increase the volume of said chamber 42 and therefore to provoke the full opening of the shutter 34 when Pc and Pt are identical.
A duct 46 extends from a tap arranged upstream of the shutter 34 to the head chamber 44.
A duct 48 extends from a tap arranged upstream of the shutter to the control chamber 42.
Each duct 46, 48 comprises a pressure reducer 46R and 48R.
The duct 48 comprises a first valve 50 which can occupy two states, passing or blocked, controlled by a first solenoid 52. By default, the first valve 50 is in the passing state. In the absence of a signal, the first solenoid 52 is deactivated and the first valve 50 is in the passing state. The shutter 34 can be in the regulated or fully open position depending on the pressure difference between Pt and Pc.
On reception of a signal S1, the first solenoid 52 is activated, provoking the change of state of the first valve 50 to the blocked state. In this case, the shutter 34 occupies the closed position since the control chamber is not pressurized.
The duct 48 comprises a coupling with a duct 54 linked to a control means 56 with a set point pressure. This control means 56 makes it possible to compare the downstream pressure Pav to a set point pressure and to adjust the pressure Pc as a function of this comparison in order to position the shutter 34 in the regulated position. This control means 56 can be activated or deactivated using a second solenoid 58.
According to one embodiment, the control means 56 comprises a reserve 60 linked to the duct 54 with an exhaust 62 and a so-called pilot actuator 64 comprising a piston 66 whose rod controls the exhaust 62. The pilot 62 comprises two chambers, a first chamber 68 containing a spring 70 and a second chamber 72 linked by a duct 74 to a tap 76 provided downstream of the shutter 34. When the pressure Pav exerts on the piston 66 a force less than that exerted by the spring 70, the rod of the piston 66 tends to keep the exhaust 62 in the closed state. On the other hand, when the pressure Pav exerts a force greater than that exerted by the spring 70, the rod of the piston 66 opens the exhaust 62 which tends to lower the pressure Pc of the control chamber and to move the shutter 34 towards the closed position.
A balance applies when the pressure Pav is equal to the set point pressure and the shutter occupies the regulated position.
To activate or deactivate the control means 56, the duct 74 comprises a second valve 78 which can occupy two states, passing or blocked, controlled by the second solenoid 58. In the absence of a signal, the second solenoid 58 is deactivated and the second valve 78 is in the blocked state. In this case, the control means 56 is deactivated and, if the first solenoid 52 is deactivated, the shutter 34 is in the fully open position.
On reception of a signal S2, the second solenoid is activated and the second valve 78 is in the passing state. In this case, the control means 56 is activated and, if the first solenoid 52 is deactivated, the shutter 34 is in the regulated position.
Thus, according to the embodiment described above, in the absence of a signal S1 and S2, the shutter is in the fully open position. On reception of the signal S1, the shutter is in the closed position. On reception of the signal S2, the shutter is in the regulated position.
According to the prior art, the pressure regulation and stop valve 32 allows a single regulation level with a set point pressure which is a function of the characteristics of the spring 70, of the volume of the reserve 60 and/or of the exhaust 62.
This type of regulation provides the following advantages:                a simple control logic which depends solely on the reception or non-reception of a signal,        a regulation control that is simple by virtue of the absence of a servo control loop in the manner of an electrohydraulic servo valve,        high reliability because of the small number of elements,        safe operation for ensuring anti-icing efficiency, the shutter 34 being in the fully open position by default.        
Even though it comprises many advantages, this type of regulation cannot be fully satisfactory because the regulation can work only according to a single pressure level.
Thus, in certain circumstances, for example for certain motorizations, it is not possible to establish a trade-off for all the flight phases, with a single regulation level, between the de-icing efficiency and the maximum temperature and pressure that can be accepted by the air inlet.
For other hot air requirements of the aircraft, such as, for example, conditioned air for the cabin, the hot air flow taken at the motorization must be regulated more flexibly, according to a number of regulation levels.
To achieve this objective, a first solution consists in using at least two hot air outlets 24, 24′ of the motorization, the two outlets being connected alternately as a function of the flight phases and/or of the outside conditions. This solution is not fully satisfactory because it leads to a further increase in the complexity of the architecture in the motorization environment.
A second solution would be to use an exchanger in order to modify at least one of the parameters (pressure/temperature) of the regulated airflow. However, this solution is relatively costly and complex, and results in increasing the embedded weight.
Finally, a third solution would be to use an electrohydraulic servo valve which makes it possible to control a hydraulic pressure (and therefore a degree of opening of the shutter) proportionally as a function of an electrical signal. This solution is not fully satisfactory because it leads to an increase in the complexity of the control logic and the servo control.